Marine Diesel Engine Auxiliaries – ‘Waste Not, Want Not' Principle

By George Backwell at April 19, 2013 23:20
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Waste heat from auxiliary marine diesel engines had not been considered much worth thinking about in the past, but times change; a significant amount of energy can now be utilised from the auxiliaries to supplement steam requirements during port stays, and also for some vessels during voyage. With high bunker prices and in challenging economic times for the shipping industry as a whole every single saved dollar counts: witness United Arab Shipping’s recent decision to retrofit all forty-eight ships in its fleet with the latest Alfa Laval Aalborg XS-TC7A auxiliary engine waste heat recovery systems.

Container Ship 'Umm Salal': Photo courtesy of United Arab Shipping Company

With its small footprint and the lowest possible weight to output ratio, the Aalborg XS-TC7A economiser optimises the use of waste heat from the auxiliary engine exhaust gases during voyage and port stays. When used in combination with a waste heat recovery system installed after the main engine, the Aalborg XS-TC7A contributes to significant reductions in oil consumption on the oil-fired boiler under most load conditions. Each unit being specially tailored to the individual ship and engine design taking into consideration the existing uptake back-pressure and other critical factors.

The manufacturers say that their Waste Heat Recovery (WHR) concept has been developed as a customised solution with special focus on energy generation compared to return on investment. They envisage a very short payback time of around to 4-6 months in optimum cases, but normal payback time is calculated to be nearer a year to 18 months, depending on the number of days the produced steam can be utilised (offset against the steam requirement from the oil fired boiler) and whatever redundancy arrangements are required.

Waste Heat Recovery System Schematic:
Image courtesy of Alfa Laval

Alfa Laval list these features of its auxiliary engine WHR system:

  • Able to supply or support the steam demand during port stay
  • Cost of steam production (energy) is nearly free
  • Financially sound investment with very short payback time
  • Adds a “green” profile to the ship
  • Lower emission tax (if introduced)
  • Less maintenance and lower operating costs for the oil-fired boiler

 “This order confirms the ship owners’ increased focus on environmental protection and interest in realizing fuel cost savings from smart solutions using the available waste heat onboard,” says Hans-Henrik Jensen, Vice President, Marine & Diesel Division, Alfa Laval. “Ship owners know and trust that Aalborg waste heat recovery systems for use after the main engines save money and reduce emissions. We now see a growing tide of ship owners like United Arab Shipping Company interested in capturing waste heat from auxiliary engines and placing their trust in the Aalborg XS-TC7A.”






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